Light-emitting element including intermediate conductive layer having an electron-injection layer with an island-like structure

ABSTRACT

When a light-emitting element having an intermediate conductive layer between a plurality of light-emitting layers is formed, the intermediate conductive layer can have transparency; and thus, materials are largely limited and the manufacturing process of an element becomes complicated by a conventional method. A light-emitting element according to the present invention is formed by sequentially stacking a pixel electrode, a first light-emitting layer, an intermediate conductive layer (including an electron injecting layer and a hole-injecting layer, one of which is island-like), a second light-emitting layer and an opposite electrode. Therefore, the present invention can provide a light-emitting element typified by an organic EL element in which a range of choice of materials that can be used as the intermediate conductive layer is broadened extremely, and which can realize a high light-emitting efficiency, a low power consumption and a high reliability, and further a display device using the light-emitting element.

This application is a continuation of application Ser. No. 11/587,843filed on Oct. 26, 2006 now U.S. Pat. No. 8,018,152 which is the USnational stage of PCT/JP2005/009312 filed May 17, 2005.

TECHNICAL FIELD

The present invention relates to an element having a structure in whichan anode, a cathode, and a thin film sandwiched between the anode andthe cathode are formed, and the thin film emits light with a phenomenoncalled electroluminescence (hereinafter, also referred to as EL)(hereinafter, referred to as a light-emitting element) and to a displaydevice provided with the light-emitting element over a substrate.Further, the present invention relates to an electronic device in whichthe light-emitting element is provided in an image-display portion.

BACKGROUND ART

An EL display is one of light-emitting devices that have attracted mostattentions as the next generation flat panel display. In alight-emitting element used for a light-emitting device, a thin filmcontaining an organic compound (hereinafter, referred to as an organicthin film) is formed between two electrodes, and current is applied tothe electrodes to generate electroluminescence. Electrons injected froma cathode and holes injected from an anode are recombined in an organicthin film to form a molecular exciton, and when the molecular excitonreturns to a ground state, photons are emitted, in other words, light isemitted. At this time, one electron and one hole are recombined to formone molecular exciton. When the molecular exciton is deactivated to theground state with luminescence, one photon of a wavelength correspondingto energy difference between the excited state and the ground state isemitted (which is called a radiation process).

In a conventional organic EL element, an organic thin film is sandwichedby a pair of an anode and a cathode. Therefore, a ratio of the number ofholes and electrons injected from the anode and the cathode(hereinafter, also referred to as carriers in the case where holes andelectrons are not distinguished) and the number of emitted photons, inother words, the quantum efficiency is not higher than 1.

As one of methods for solving such a constraint, there is proposed amethod for forming an intermediate conductive layer in an element, inaddition to the cathode and anode (Reference 1: Japanese PatentLaid-Open No. H11-329748, pp. 6 to 7 and FIG. 3).

According to Reference 1, an organic EL element is proposed, in which anAlq:Li layer 13 including Alq (Al complex of 8-hydroxyquinoline) and Li,and an In—Zn—O (indium.zinc oxide) layer 14 are formed in an elementsandwiched by a pair of an anode 11 and a cathode 12, and organic layers15 and 16 are formed on the opposite sides, namely, the anodes side andthe cathode side of the layers (FIG. 14). Note that reference numeral 17denotes an interlayer insulating film. Here, the layer in which theAlq:Li layer and the In—Th—O layer are stacked is defined as anintermediate conductive layer. In an organic EL element having such astructure, holes and electrons are injected from an anode and a cathode,respectively, as in a general organic EL element. The holes andelectrons are transported to the cathode side and the anode side,respectively. The characteristic point here is that carriers aresupplied also from the intermediate conductive layer. In other words,electrons are injected into the organic layer 15 from the anode side(Alq:Li layer 13 side) of the intermediate conductive layer, and at thesame time, holes are injected into the organic layer 16 from the cathodeside (In—Zn—O layer 14 side) of the intermediate conductive layer. Inthe organic layer 15 on the anode side, holes injected from the anode 11and electrons injected from the intermediate conductive layers 13 and 14are recombined to generate a molecular exciton, which leads toluminescence (light-emission). Similarly, in the organic layer 16 on thecathode side, electrons injected from the cathode 12 and holes injectedfrom the intermediate conductive layers 13 and 14 are recombined togenerate a molecular exciton, and light-emission is obtained by theradiation process of the molecular exciton.

By the above described mechanism, this organic EL element can providealmost the same effect as the case where general organic EL elements arearranged serially. In other words, although the driving voltage of theorganic EL element becomes almost twice higher than a general organic ELelement, the number of obtained photons with the same current densitybecomes twice more than that of the general organic EL element.Therefore, the quantum efficiency almost doubles. It is also possiblethat the quantum efficiency can be further increased by applying thismethod. For example, two intermediate conductive layers and threeorganic thin films are arranged alternately, thereby obtaining almostthe same effect as that obtained when three organic EL elements arearranged serially. Therefore, although the driving voltage becomesalmost three times higher, the quantum efficiency becomes almost threetimes higher at the same time. Consequently, a high-luminance organic ELelement can be provided.

The requirement for realizing this idea is that the intermediateconductive layer sandwiched by organic layers is transparent. A materialthat can be used as the intermediate conductive layer is limited so asto fulfill this requirement. Until now, there have been proposed variousmaterials. However, materials that have been used actually are limitedto the followings: 1: a stacked layer of a mixed layer containing anelectron transporting compound such as Alq or bathocuproin (BCP) and anelectron injecting compound such as an alkali metal and a transparentelectrode such as ITO (indium tin oxide) or IZO (indium zinc oxide); 2:a stacked layer of the mixed layer containing the electron transportingcompound and the electron injecting compound and a metal oxide; 3: astacked layer of the mixed layer containing the electron transportingcompound and the electron injecting compound and an electron-acceptingorganic compound, and the like.

By using the above described materials, the intermediate conductivelayer can keep transparency; however, the material is largely limitedand a manufacturing process of an element becomes also complicated. Forexample, according to the method described in Reference 1, in general,an organic layer is formed by a vacuum vapor deposition method. By thismethod, a mixed layer of an electron transporting compound and anelectron injecting compound can be easily formed on the organic layer.However, a transparent electrode such as ITO or IZO cannot be formed bya vacuum vapor deposition method and formed by a sputtering method.Therefore, such transparent electrodes should be formed after an elementis transferred into a chamber for forming a film by a sputtering methodfrom a chamber for an evaporation method, and thus the manufacturingprocess becomes complicated.

Further, as for the technique related to Reference 1, there are known anorganic EL (electroluminescence) element, as shown in References 2(Japanese Patent Laid-Open No. 2003-45676 p. 1 FIG. 3) and 3 (JapanesePatent Laid-Open No. 2003-272860 p. 1 FIG. 8), in which a plurality oflight-emitting units are separated by one layer forming an equipotentialsurface, and an organic EL element having a structure in which aconductor thin film layer is interposed between two organic EL layers asshown in Reference 4 (Japanese Patent Laid-Open No. 2003-264085 p. 11FIG. 7).

DISCLOSURE OF INVENTION

The present invention has been made in view of the above describedproblems. It is an object of the present invention to provide alight-emitting element typified by an organic EL element in which arange of choice of a material that can be used as an intermediateconductive layer sandwiched by organic thin films functioning as alight-emitting layer is broadened extremely, and which can realize ahigh light-emitting efficiency, a low power consumption and a highreliability, and further a display device (light-emitting device) usingthe light-emitting element.

One feature of a light-emitting element according to the presentinvention is that it has a stacked structure in which a first electrode,a first light-emitting layer, an intermediate conductive layer, a secondlight-emitting layer, and a second electrode, where the intermediateconductive layer comprises an electron injecting layer and ahole-injecting layer that is in contact with the electron injectinglayer, and where at least one of the electron-injecting layer and thehole-injecting layer is an island-like layer. Herein, the firstelectrode may have a function of an anode or a cathode. On the otherhand, the second electrode may have an opposite polarity of the firstelectrode and may be an anode or a cathode. In addition, an island-likeelectron-injecting layer and the hole-injecting layer are collectivelyreferred to as the intermediate conductive layer, and the layer canselect appropriately a stacking sequence thereof depending on thepolarities of the first electrode and the second electrode. Instead offorming the election-injecting layer as island-like layer, thehole-injecting layer may be island-like. Alternatively, the both layersmay be island-like. Note that “island-like” herein means that elements(layers) are dotted in an island-shaped state and may be dot-like,protrusion-like, cluster-like (such dots or protrusions aggregates) orthe like, and the shape is not limited. Further, “the island-like layer”has at least one island-like structure. Arrangement in an island-shapedmanner/state may be at random or intentional. In any cases, it may haveany structure as long as the electron-injecting layer of theintermediate conductive layer is in contact with a light-emitting layeron the anode side, and the hole-injecting layer is in contact with alight-emitting layer on the cathode side, and further theelectron-injecting layer and the hole-injecting layer are in contactwith each other. Here, the first electrode is a pixel electrode and thesecond electrode is an opposite electrode.

In a light emitting element according to the present invention describedabove, a third light-emitting layer may be formed over the secondlight-emitting layer with an intermediate conductive layer to be formedanew (an electron-injecting layer and a hole-injecting layer)therebetween. In this case, at least one of the electron-injecting layerand the hole-injecting layer contained in at least one of theintermediate conductive layers preferably has an island-like structure.That is, when a light-emitting element has three light-emitting layers,two intermediate conductive layers are sandwiched; however, at least oneof the electron-injecting layer and the hole-injecting layer that existin at least one of the two intermediate conductive layers is preferablyisland-like. Note that the number of light-emitting layers andintermediate conductive layers that are stacked is not limited inparticular. For example, when a light-emitting element has fourlight-emitting layers, three intermediate conductive layers aresandwiched in the light-emitting layer. Alternatively, when alight-emitting element has five light-emitting layers, four intermediateconductive layers are sandwiched in the light-emitting layer.

Specifically, the light-emitting element includes a structure in which afirst electrode, a plurality of light-emitting layers, a plurality ofintermediate conductive layers sandwiched by the plurality oflight-emitting layers, a second electrode are stacked. The intermediateconductive layer includes an electron injecting layer and a holeinjecting layer that is in contact with the electron injecting layer,and at least one of the electron injecting layer and the hole injectinglayer is an island-like layer.

Further specifically, the light emitting element is formed bysequentially stacking an n number of light-emitting layers (where n isan integer equal to or greater than 2) comprising a first through ann-th light-emitting layers between a first electrode and a secondelectrode, and an intermediate conductive layer is formed between a k-thlight-emitting layer (where k is an integer of 1≦k≦(n−1)) and a (k+1)thlight-emitting layer. Further, the intermediate conductive layercomprises an electron injecting layer and a hole-injecting layer that isin contact with the electron injecting layer, and at least one of theelectron-injecting layer and the hole-injecting layer is an island-likelayer. Here, the first electrode is a pixel electrode and the secondelectrode is an opposite electrode.

A display device according to the present invention includes atransistor formed over a substrate, and a light-emitting elementconnected to the transistor through an interlayer insulating film,wherein the light-emitting element has a first electrode, a firstlight-emitting layer, an intermediate conductive layer, a secondlight-emitting layer, and a second electrode, where the intermediateconductive layer comprises an electron injecting layer and ahole-injecting layer that is in contact with the electron injectinglayer, and at least one of the electron-injecting layer and thehole-injecting layer is an island-like layer. Herein, the firstelectrode of the light-emitting element may have a function of an anodeor a cathode. On the other hand, the second electrode may have anopposite polarity of the first electrode and may be an anode or acathode. In addition, an island-like electron-injecting layer and thehole-injecting layer are collectively referred to as the intermediateconductive layer, and the layer can select appropriately a stackingsequence depending on the polarities of the first electrode and thesecond electrode. Instead of forming the electron-injecting layer as anisland-like layer, the hole-injecting layer may be island-like.Alternatively, the both layers may be island-like. In any cases, it mayhave any structure as long as the electron-injecting layer of theintermediate conductive layer is in contact with a light-emitting layeron the anode side, and the hole-injecting layer is in contact with alight-emitting layer on the cathode side, and further theelectron-injecting layer and the hole-injecting layer are in contactwith each other. Here, the first electrode is a pixel electrode and thesecond electrode is an opposite electrode.

In a light emitting element according to the present invention describedabove, a third light-emitting layer may be formed over the secondlight-emitting layer with an intermediate conductive layer to be formedanew (an electron-injecting layer and a hole-injecting layer)therebetween. In this case, at least one of the electron-injecting layerand the hole-injecting layer contained in at least one of theintermediate conductive layers preferably has an island-like structure.That is, when a light-emitting element has three light-emitting layers,two intermediate conductive layers are sandwiched; however, at least oneof the electron-injecting layer and the hole-injecting layer that existin at least one of the two intermediate conductive layers is preferablyisland-like. Note that the number of light-emitting layers andintermediate conductive layers that are stacked is not limited inparticular. For example, when a light-emitting element has fourlight-emitting layers, three intermediate conductive layers aresandwiched in the light-emitting layer. Alternatively, when alight-emitting element has five light-emitting layers, four intermediateconductive layers are sandwiched in the light-emitting layer.

Specifically, a display device includes a transistor formed over asubstrate, and a light-emitting element connected to the transistorthrough an interlayer insulating film. The light-emitting element has astructure in which a first electrode, a plurality of light-emittinglayers, a plurality of intermediate conductive layers sandwiched by theplurality of light-emitting layers, a second electrode are stacked. Theintermediate conductive layer includes an electron injecting layer and ahole injecting layer that is in contact with the electron injectinglayer, and at least one of the electron injecting layer and the holeinjecting layer is an island-like layer.

Further specifically, a display device according to the presentinvention includes a transistor formed over a substrate, and alight-emitting element connected to the transistor through an interlayerinsulating film. The light emitting element is formed by sequentiallystacking an n number of light-emitting layers (where n is an integerequal to or greater than 2) comprising a first through an n-thlight-emitting layers between a first electrode and a second electrode,and an intermediate conductive layer is formed between a k-thlight-emitting layer (where k is an integer of 1≦k≦(n−1)) and a (k+1)thlight-emitting layer, where the intermediate conductive layer comprisesan electron injecting layer and a hole-injecting layer that is incontact with the electron injecting layer, and at least one of theelectron-injecting layer and the hole-injecting layer is an island-likelayer. Here, the first electrode is a pixel electrode and the secondelectrode is an opposite electrode.

One feature of a light-emitting element according to the presentinvention is that in an EL element having a plurality of light-emittinglayers between a pixel electrode and an opposite electrode, anintermediate conductive layer is provided between each light-emittinglayer, and at least one of an electron-injecting layer and ahole-injecting layer constituting an intermediate conductive layer (atleast one intermediate conductive layer in the case of forming pluralintermediate conductive layers) is not film-like but island-like. Byadopting the structure, the following effects can be obtained.

There is an advantageous effect that transparency of a material for theelectron-injecting (or hole-injecting) layer of an intermediateconductive layer is not required to be considered. Even when using anintermediate conductive layer that has a large extinction coefficient ina visible band, absorption itself can become vanishingly small byforming the layer into island-like shape. Therefore, light from thelight-emitting layer is mostly not absorbed into the intermediateconductive layer.

In addition, in case that an organic material (especially aromaticcompound) is used as an intermediate conductive layer, the crystallinityof the intermediate conductive layer become high unless a moleculardesign is positively conducted thereto. Thus, characteristics of anelement change drastically. At worst, electricity is conducted betweenthe both electrodes, and the both electrodes are short-circuited.However, by adopting a structure according to the present invention,even if individual island-like layers are crystallized, the influence onthe light-emitting element becomes small or can be ignored and thechange of the light-emitting element characteristics due tocrystallization can be suppressed.

Further, it is clear that the slight amount of material is needed to beused, and thus the manufacturing time of an element can be shortened,which results in reduction of cost. As described above, various effectscan be obtained by forming a part of intermediate conductive layer to beisland-like instead of to be film-like as conventionally.

Further, a display device according to the present invention has alight-emitting element that provides the above described operationeffects; therefore various operation effects such as highlight-extraction efficiency, low power-consumption, low cost and longlife can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 shows a structure of a light-emitting element according to thepresent invention;

FIGS. 2A and 2B each show a structure of a light-emitting elementaccording to the present invention;

FIGS. 3A and 3B are an equivalent circuit diagram (of two transistors)of a pixel region in a display device according to the present inventionand a top view of a display panel of the display device, respectively;

FIGS. 4A and 4B are each a cross-sectional view of a display deviceaccording to the present invention;

FIGS. 5A and 5B are each an equivalent circuit diagram (of threetransistors and of four transistors) of a pixel region in a displaydevice according to the present invention;

FIGS. 6A to 6D each show a structure in which a wiring has a stackedstructure;

FIGS. 7A to 7F each show an electronic device provided with a displaydevice according to the present invention;

FIG. 8 is a block diagram showing main constituents of a televisiondevice using a display device according to the present invention;

FIGS. 9A and 9B each show an ID card using a display device according tothe present invention;

FIG. 10 is a top view of a light-emitting device according to thepresent invention;

FIG. 11 is a circuit diagram explaining operation of a pixel in alight-emitting device according to the present invention;

FIG. 12 is a top view of a pixel area in a light-emitting deviceaccording to the present invention;

FIG. 13 shows operation of a frame period with time;

FIG. 14 shows a structure of a conventional light-emitting device;

FIG. 15 shows a method for selecting a plurality of gate signal lines atthe same time in one horizontal period; and

FIG. 16 shows a structure of a light-emitting element according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention will hereinafter bedescribed with reference to the accompanying drawings. The presentinvention can be carried out in many different modes, and it is easilyunderstood by those skilled in the art that modes and details hereindisclosed can be modified in various ways without departing from thespirit and the scope of the present invention. It should be noted thatthe present invention should not be interpreted as being limited to thedescription of the embodiments to be given below. For example,characteristic parts of Embodiments and Examples to be describedhereinafter can be combined and implemented. Note that the samereference numerals are used for the same portions in the structure ofthe present invention to be described hereinafter.

Embodiment of the present invention is described with reference toFIG. 1. Note that FIG. 1 shows an element structure in which twolight-emitting layers are separated by one intermediate conductivelayer; however, the number of light-emitting layers is not limited. Inaddition, by the structure, the number of the intermediate conductivelayers is fewer than the total number of the light-emitting layers byone.

In an organic EL element, light is needed to be extracted outside, andthus at least one of an anode and a cathode is required to betransparent. Hereinafter, a light-emitting element in which over asubstrate, a transparent anode is formed on the substrate side and lightcan be extracted from the anode side, namely a bottom-emission typelight emitting element is described.

A substrate 101 for supporting a light-emitting element and the like isprepared. Paper, plastic resin and the like as well as quartz or glasscan be used as the substrate 101. In addition, a substrate over which athin film transistor (TFT) has been formed in advance can also be used.In this embodiment, since a transparent anode 102 is formed over thesubstrate and light is extracted to the substrate side, it is preferablethat the substrate transmits visible light. As the transparent anode, aconductive metal oxide such as ITO or IZO is preferable. Such conductivemetal oxide films are formed by a sputtering method in a conventionalmanner; however, may be formed by a sol-gel method. In addition, a metalhaving a high work function such as gold can also be used as a materialother than the metal oxide. In this case, an ultra thin film is formedin consideration of a light-transmitting property.

A first light-emitting layer 103 is formed on the anode that has beenformed in this manner. This light-emitting layer is formed primarilyusing an organic compound. The light-emitting layer may be formed usinga thin film of a single composition. For example, typical metalcomplexes are given, such as tris(8-quinolinolate) aluminum (Alq₃),tris(4-methyl-8-quinolinolate) aluminum (Almq₃),bis(10-hydroxybenzo[h]-quinolinato) beryllium (BeBq₂),bis(2-methyl-8-quinolinolate)(4-phenylphenolate)aluminum (BAlq),bis[2-(2-hydroxyphenyl)-benzooxazolate]zinc (Zn(BOX)₂), andbis[2-(2-hydroxyphenyl)-benzothiazolate]zinc (Zn(BTZ)₂). Further, acompound containing hydrocarbon, such as 9,10-diphenylanthracene or4,4′-bis(2,2-diphenyl ethenyl) biphenyl are also preferable.

Further, the light-emitting layer may be a mixed layer of a plurality ofmaterials. Luminous efficiency can be increased by adding a slightamount of a fluorescent material or a phosphorus material into the abovedescribed light emitter. As the fluorescent material, a coumarinderivative, a quinacridon derivative, an acridone derivative, a pyrenederivative, a perylene derivative, an anthracene derivative, a pyrronederivative and the like are cited. As the phosphorus material, tripletlight-emitting materials such as tris (2-phenylpyridine) iridium(hereinafter, Ir(ppy)₃) and2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin-platinum (hereafter,PtOEP), transition metal complexes of Ir, Ru, Ph, Pt or a rare earthmetal or the like can be cited.

On the other hand, the light-emitting layer may be a film having astacked structure. By adopting the stacked structure, injection balanceof electrons and holes can be controlled more easily than by adoptingthe above-described light-emitting layer of a single composition or amixed composition. Accordingly, the luminous efficiency can be moreenhanced. For example, a hole-transporting layer for efficientlycarrying injected holes into the light-emitting layer, and anelectron-transporting layer for efficiently carrying injected electronsinto the light-emitting layer are preferably provided in addition to theabove-described light-emitting layer of a single composition or a mixedcomposition. In some cases in this specification, layers including suchhole transporting layer, electron transporting layer or hole injectinglayer and electron injecting layer in addition to a light-emitting layeris collectively referred to as a light-emitting layer. As materialssuitable for the hole transporting layer, a compound comprising anaromatic amine (that is, one having a benzene ring-nitrogen bondtherein) is preferred. As other widely-used materials, star burstaromatic amine compounds are also used, such as4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl, derivativesthereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl,4,4′,4″-tris[N,N-diphenyl-amino]triphenylamine, and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine. The typical metal complexes are often used as materials suitablefor the electron transporting layer. As other materials, triazolederivatives such as3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazoleand phenanthroline derivatives such as bathophenanthroline andbathocuproin, or benzoxazole derivatives such asbis(5-methylbenzoxazol-2-yl)stilbene may be also used.

A film formation method may be a wet method such as a spin coatingmethod, a dip coating method, a spray method as well as vacuum vapordeposition.

Then, an intermediate conductive layer is formed. In this embodiment,since a light-emitting element is formed on the anode side, anelectron-injecting layer 104 is formed first. Herein, theelectron-injecting layer 104 may be formed to be island-like as shown inthe drawing. It is preferable to employ e.g., a vapor deposition methodto form the island-like electron-injecting layer. In this case,specifically, after a sublimated material forms a nucleus, the nucleusis grown. The vapor deposition process may be stopped before clustersgrown from different nucleuses binds with one another. In addition, asmaterials suitable for the electron-injecting layer 104, metals having alow work function and metal compounds thereof are given. Mg—Ag alloy,Al—Li alloy, Mg—Li alloy, Ca₃N₂, Mg₃N₂ and the like are given asexamples thereof. Further, an organic semiconductor doped with a donoris also an example, as well as such metals. As preferable examples ofthe organic semiconductor, a compound to serve as an acceptor is given,and an electron-transporting material that is often used in alight-emitting element may be adopted. For example, typical metalcomplexes typified by Alq, phenanthroline derivatives, triazinederivatives, oxazole derivatives, quinoline derivatives, quinoxalinederivatives and the like are given. Further, electron-acceptingcompounds such as tetracyano quinodimethane, tetracyanoethylene, andtetrachloroquinone are also preferable examples. Condensed aromatichydrocarbon such as rubrene and perylene derivatives is nominated asother examples. Conductive materials such as graphite can also beemployed. Further, conjugated polymer (high molecular weight compound)such as polyphenylene vinylene, polyphenylene ethynylene or polypyridinecan also be used. Note that high molecular weight compound (polymer) ispreferably used also for the light-emitting layer in this case. Further,it is preferable to design so that the high molecular weight compoundused for the light-emitting layer is not dissolved in a solvent fordissolving a high molecular weight compound used for forming theintermediate conductive layer. This is made in order to prevent thethin-film structure from being broken as the result of dissolution ofthe light-emitting layer by the solvent for dissolving high molecularweight compound material, because the high molecular weight compoundmaterial is formed by a wet method in a conventional manner. Metalshaving a low work function such as alkali metal and alkaline earth metalare preferable for the donor added into the organic semiconductor.Electron excess type organic compounds such as tetrathiafulvalene mayalso be used. Note that it is essential that the acceptor property ofsuch organic semiconductors is strong, because the donor property of theelectron excess type organic compounds is smaller than that of alkalimetals or alkaline earth metals. As other examples than organicsemiconductors, alkali metals, alkaline earth metals, rare earth metalsand compounds containing these metals are preferable. Specifically,calcium fluoride, lithium oxide, lithium chloride, lithium fluoride,magnesium fluoride, barium oxide are given.

In this way, the electron-injecting layer 104 that is film-like orisland-like is formed on the first light-emitting layer 103. Theelectron-injecting layer 104 may be film-like or island-like; however,the island-like electron-injecting layer is more preferable than thefilm-like one, because light can be extracted more efficiently. By theisland-like electron-injecting layer 104, defects of the light-emittingelement due to crystallization are difficult to generate, even if asubstance to easily be crystallized is used.

As the intermediate conductive layer, the electron-injecting layer 104is formed first and then a hole-injecting layer 105 is formed. Metalssuch as gold, aluminum, platinum, copper, and nickel are given asmaterials suitable for the hole-injecting layer. The metals have a highwork function, and thus holes can be easily injected. These materialscan hold transparency only when they are ultra thin films. However, asproposed in the present invention, the electron-injecting layer of theintermediate conductive layer is formed to be film-like, and then thehole-injecting layer is formed to be island-like. As the result thereof,the intermediate conductive layer itself can hold transparency (FIG. 2Aand FIG. 2B).

Various metal-containing compounds can be used as materials for formingthe hole-injecting layer as other examples. For example, transitionmetal oxides such as cobalt oxide, titanium oxide, niobium oxide, nickeloxide, neodymium oxide, vanadium oxide, beryllium aluminum oxide,molybdenum oxide, lanthanum oxide, ruthenium oxide, rhenium oxide aregiven. Preferably, oxides, nitrides or halides of transition metal of 4to 7 groups may be used. These metal oxides, nitrides, halides or thelike conduct an electron transfer reaction at the interface with thelight-emitting layer, and forms electric charges-transfer complex. Thus,the materials can inject holes by themselves. In addition, a suitabledonor may be added into these materials to actively form electriccharges-transfer complex. Electron excess type organic compounds such astetrathiafulvalene or carbazole derivatives are given as the donor. Inaddition, aromatic amine group that is classified into, so-called, holetransporting materials and hole injecting materials of organic ELelements are also preferable. Specifically, TPD, NPB and the like aregiven.

The hole-injecting layer 105 may be film-like or island-like; however,light can be extracted more efficiently by adopting the island-likehole-injecting layer 105. By the island-like hole-injecting layer 105,defects of the light-emitting element due to crystallization aredifficult to generate, even if a substance to easily be crystallized isused.

Note that when it is difficult to maintain transparency unless theelectron-injecting layer of the intermediate conductive layer is anultra thin film, the electron-injecting layer is formed to beisland-like, and then the hole-injecting layer is formed to befilm-like. As the result thereof, the intermediate conductive layeritself can hold transparency.

A second light-emitting layer 106 is formed on the thusly formedintermediate conductive layer. This light-emitting layer may have thesame structure as the first light-emitting layer or a differentstructure. Moreover, color of light-emission may be the same ordifferent. When the first light-emitting layer and the secondlight-emitting layer emit light of different colors that arecomplementary colors of each other, white light-emission can beobtained. For example, as shown in FIG. 2A, it may be designed that thefirst light-emitting layer 103 emits light of blue and the secondlight-emitting layer 106 emits light of red. Specifically, the firstlight-emitting layer is formed using aromatic hydrocarbon compoundstypified by anthracene derivatives such as 9,10-diphenylanthracene orthe like, whose luminescence center is observed in about 450 to 500 nm.The second light-emitting layer may be formed using materials usingso-called DCM such as4-(dicyanomethylene)-2-[p-(dimethylamino)styryl]-6-methyl-4H-pyran,aromatic hydrocarbon compound such as rubrene, or the like whoseluminescence center is observed in about 600 to 650 nm. Alternatively,as shown in FIG. 2B, three organic thin films (a third light-emittinglayer 108 is added to the first and second light-emitting layers) areformed and each of them are designed to emit primary colors of blue,green and red, thereby obtaining light-emission of white colorsimilarly. Thus, it can be applied to lightning. As materials foremitting green light, a typical metal complex such as Alq, andfluorescent material such as quinacridon and coumarin are preferred. Aphosphorescence material such as Ir(ppy)₃ can be also used.

A cathode 107 is formed on the second light-emitting layer 106 (or thethird light-emitting layer 108). In this embodiment, since light isextracted from the anode side, the cathode may be non-transparent.Specifically, aluminum or a magnesium-silver alloy may be employed. Notethat the electron-injecting layer may be provided before forming thecathode so as to promote electron-injection from the cathode. For theelectron-injecting layer, alkali metal salt or alkaline earth metal saltsuch as calcium fluoride or lithium fluoride, lithium oxide or lithiumchloride may be used.

Note that in this embodiment, the anode 102 and the cathode 107 may becounterchanged, and at this time correspondingly, the electron-injectinglayer and the hole-injecting layer are preferably stacked reversely.

In addition, the number of the light-emitting layers and theintermediate conductive layers that are stacked is not limited inparticular. Specifically, the light-emitting element includes astructure in which a first electrode, a plurality of light-emittinglayers, a plurality of intermediate conductive layers sandwiched by theplurality of light-emitting layers, a second electrode are stacked. Theintermediate conductive layer includes an electron injecting layer and ahole injecting layer that is in contact with the electron injectinglayer, and at least one of the electron injecting layer and the holeinjecting layer is an island-like layer. As shown in FIG. 16, forexample, the light emitting element is formed by sequentially stackingan n number of light-emitting layers (where n is an integer equal to orgreater than 2) comprising a first light-emitting layer 203 through ann-th light-emitting layer 213 between the anode 102 and the cathode 107.Then, a first electron injecting layer 204 and a first hole-injectinglayer 205 through a (n−1)th electron injecting layer 211 and a (n−1) thhole-injecting layer 212 are formed between the light-emitting layers.That is, the intermediate conductive layer is formed between a k-thlight-emitting layer 207 (where k is an integer of 1≦k≦(n−1)) and a(k+1)th light-emitting layer 210. The intermediate conductive layercomprises a k-th electron injecting layer 208 and a k-th hole-injectinglayer 209 that is in contact with the electron injecting layer 208.According to this embodiment of the invention, the k-th hole-injectinglayer 209 is an island-like layer.

EXAMPLE 1

In this example, the structure of an active matrix display device (alsoreferred to as an active matrix light-emitting device) using alight-emitting element according to Embodiment is explained withreference to FIGS. 3A, 3B 4A and 4B. A display device according to thisexample has a plurality of pixels 310 including a plurality of elementsin a region formed by the intersection of a source line Sx (x is anatural number, 1≦x≦m) with a gate line Gy (y is a natural number,1≦x≦n) with an insulator interposed therebetween (FIG. 3A). The pixel310 has a light-emitting element 313, a capacitor element 316 and twotransistors. One of the two transistors is a transistor for switching311 (switching transistor) for controlling input of a video signal tothe pixel 310, and the other is a transistor for driving 312 (drivingtransistor) for controlling light emission and non-light emission of thelight-emitting element 313. The capacitor element 316 serves to holdgate-source voltage of the transistor 312.

Agate electrode of the transistor 311 is connected to the gate line Gy.One of a source electrode and a drain electrode is connected to thesource line Sx, and the other is connected to a gate electrode of thetransistor 312. One of a source electrode and a drain electrode of thetransistor 312 is connected to a first power source 317 via a powersource line Vx (x is a natural number, 1≦x≦1), and the other isconnected to a pixel electrode of the light-emitting element 313. Anopposite electrode (cathode 107) of the light-emitting element 313 isconnected to a second power source 318. The capacitor element 316 isprovided between the gate electrode and the source electrode of thetransistor 312. The transistors 311 and 312 may have an n-typeconductivity or a p-type conductivity. In the structure shown in thedrawing, the transistor 311 is an n-channel type and the transistor 312is a p-channel type. The electric potentials of the first power source317 and the second power source 318 are not especially restricted. Thefirst power source 317 and the second power source 318 are set to haveelectric potentials different from each other so that forward biasvoltage or reverse bias voltage is applied to the light-emitting element313.

A semiconductor constituting parts of the transistors 311 and 312 may bean amorphous semiconductor (amorphous silicon), a microcrystallinesemiconductor, a crystalline semiconductor, an organic semiconductor, orthe like. The microcrystnlline semiconductor may be formed using silanegas (SiH₄) and fluorine gas (F₂), or silane gas (SiH₄) and hydrogen gas.Alternatively, the microcrystalline semiconductor may be formed byforming a thin film using such a gas and irradiating the thin film withlaser light. The gate electrodes of the transistors 311 and 312 areformed as a single layer or a stacked layer of a conductive material.For instance, the stacked layer is preferably formed to have any one ofthe following structures: a stacked layer structure formed by stackingtungsten (W) over tungsten nitride (WN), a stacked layer structureformed by stacking aluminum (Al) and molybdenum (Mo) over Mo, and astacked layer structure formed by stacking Mo over molybdenum nitride(MoN).

FIG. 3B is a top view of a display panel of a display device accordingto this example. In FIG. 3B, a light-emitting region 400 having aplurality of pixels (pixels 310 shown in FIG. 3A) includinglight-emitting elements (also, herein referred to as a pixel region or adisplay region), gate drivers 401 and 402, a source driver 403, and aconnection film 407 such as an FPC are formed over a substrate 405. Theconnection film 407 is connected to an IC chip or the like.

FIGS. 4A and 4B are cross-sectional views of a display panel taken alongthe line A-B in FIG. 3B. FIG. 4A shows a light-emitting region 400 of atop emission light-emitting device to which a light-emitting elementaccording to the present invention is applied, whereas FIG. 4B shows alight-emitting region 400 of a dual emission light-emitting device towhich a light-emitting element according to the present invention isapplied. In the dual emission light-emitting device, light can beextracted from the opposite sides (top side and bottom side).

The structure shown in FIG. 4A is described first. In FIG. 4A, thetransistor 312 and the light-emitting element 313 provided in thelight-emitting region 400 (the transistor 311 in FIG. 3A is omittedhere), and an element group 410 provided in the source driver 403 areshown. Reference numeral 316 denotes a capacitor element. A sealingagent 408 is provided around the periphery of the light-emitting region400, the gate drivers 401 and 402, and the source driver 403. Thus, thelight-emitting element 313 is sealed by the sealing agent 408 and anopposite substrate 406. The sealing process is a process for protectingthe light-emitting element 313 from water, and a cover material (such asglass, ceramic, plastic or metal) is used for the sealing process.Alternatively, thermosetting resin or ultraviolet curing resin may beused in the sealing process, further a thin film having high barrierproperty such as a metal oxide or nitride may be used.

As for the sealing agent 408, ultraviolet curing or thermosetting epoxyresin may be used, typically. An ultraviolet epoxy resin (2500 Clearmanufactured by ElectroLite Corporation) having high heat resistance, arefractive index of 1.50, a viscosity of 500 cps, a shore D hardness of90, a tensile intensity of 3000 psi, a Tg point of 150° C., a volumeresistance of 1×10¹⁵ Ω·cm, and a resistance voltage of 450 V/mil is usedhere.

The cathode 107 of the light-emitting element 313 is connected to thesecond power source 318 in FIG. 3A. An element formed over the substrate405 is preferably made from a crystalline semiconductor (polysilicon)having better characteristics such as mobility than that of an amorphoussemiconductor. In this instance, a monolithic device in which elementsare formed on the same surface can be obtained. A panel having theforegoing structure can be reduced in its size, weight, and thicknessbecause the number of external ICs to be connected is reduced.

The light-emitting region 400 may include a transistor having anamorphous semiconductor (amorphous silicon) formed over an insulatingsurface as a channel portion. The gate drivers 401 and 402 and thesource driver 403 may include IC chips. The IC chips may be attachedonto the substrate 405 by a COG method or attached onto the connectionfilm 407 to be connected to the substrate 405. The amorphoussemiconductor can be readily formed by using a CVD method over a largesubstrate. Further, a panel can be provided at low cost because aprocess of crystallization is not required. When a conductive layer isformed by a droplet discharging method typified by an ink-jet method,the panel can be provided at much lower cost.

In the structure shown in FIG. 4A, first and second interlayerinsulating films 411 and 412 are formed over the transistor 312 and theelement group 410. Further, a wiring 414 is formed through an openingportion that is provided in the first and second interlayer insulatingfilms 411 and 412. The wiring 414 serves as a source wiring, a drainwiring or the like of the transistor 312 and the element group 410. Itis preferable to use an alloy containing aluminum and nickel as thewiring 414. The alloy may contain carbon, cobalt, iron, silicon, or thelike. The alloy is preferably mixed, for example, with carbon of 0.1 to3.0 atomic % at rate of content, at least one element of nickel, cobalt,iron of 0.5 to 7.0 atomic %, and silicon of 0.5 to 2.0 atomic %. Thesematerials have a characteristic of having a low resistance value of 3.0to 5.0 Ωcm.

In the case that Al is used as the wiring 414, there is a problem ofgenerating corrosion with an anode 102, for example, ITO. Despite of theproblem, favorable contact to ITO can be obtained by adopting a stackedlayer structure of sandwiching the Al (or Al—Si alloy) between Ti orbetween TiN. For example, a stacked layer structure of sequentiallystacking Ti, Al, and Ti may be formed. On the other hand, the foregoingAl—C alloy, Al—C—Ni alloy, or the like has oxidation-reduction potentialthat is substantially equal to that of a transparent conductive filmsuch as ITO; therefore the Al—C alloy or the Al—C—Ni alloy can makedirect contact to ITO or the like without having a stacked layerstructure (without being sandwiched between Ti, TiN, or the like). Thewiring 414 can be formed using a target material of the foregoing alloysby a sputtering method. When etching is performed to the alloys usingresist as a mask, a wet etching method is preferably used, and at thistime phosphoric acid or the like can be used as an etchant. The wiringconnected to the second power source 318 can also be formed in the samemanner as that of the wiring 414.

The anode 102 is formed to be in contact with the wiring 414. Note thatthe order of stacking the wiring 414 and the anode 102 is not limitedthereto. A reflective conductive film is used as the anode 102 becausethe light-emitting device shown in FIG. 4A is a top emission type. Forexample, a film including an element selected from Cr, Ti, TiN, TiSixNy,Ni, W, WSix, WNx, WSixNy, NbN, Pt, Zn, Sn, In, and Mo, of an alloymaterial or a compound material containing the element as the maincomponent or a stacked layer of there films may be used.

In FIG. 4A, the anode 102 extends as far as the region where thecapacitor element 316 is formed and the anode 102 serves also as acapacitor electrode of the capacitor element 316. Of course, a wiring tofunction as a capacitor electrode may be formed separately (in general,it is formed at the same time as the wiring 414).

The materials of the first and second interlayer insulating films arenot especially restricted. For instance, the first interlayer insulatingfilm may be made from an inorganic material, and the second interlayerinsulating film may be made from an organic material, and at this timesilicon oxide, silicon nitride, silicon oxynitride, a film includingcarbon such as DLC or carbon nitride (CN), PSG (phosphorus glass), BPSG(boron phosphorus glass), an alumina film; or the like can be used asthe inorganic material. As for the formation method, a plasma CVDmethod, a low pressure CVD (LPCVD) method, an atmospheric plasma method,or the like can be used. Alternatively, an SOG film (for example, a SiOxfilm including an alkyl group) formed by a coating method can be used.In this example, the first interlayer insulating film 411 formed overthe transistor 312 is formed as far as possible, because the firstinterlayer insulating film 411 has a barrier function to preventimpurities such as Na, O₂ and water from entering the transistor 312(which is referred to as a cap insulating film, since it has thefunction). However, it is possible that the first interlayer insulatingfilm is omitted.

A photosensitive or non photosensitive organic material such aspolyimide, acrylic, polyamide, resist materials, or benzocyclobutene; orheat-resisting organic resin such as siloxane can be used as the organicmaterial. As the method for forming the interlayer insulating films, aspin coating method, a dipping method, a spray coating method, a dropletdischarging method (such as an ink-jet method, a screen printing method,an offset printing method), a doctor knife, a roll coater, a curtaincoater, a knife coater, or the like can be used depending on thematerials. The first and second interlayer insulating films can beformed by stacking the foregoing materials.

A bank layer 409 (also referred to as mound, bank or barrier) is formedaround the periphery of the anode 102. As the bank layer 409, aphotosensitive or non photosensitive organic resin material such aspolyimide, acrylic, polyamide, polyimide amide, resist materials, orbenzocyclobutene; or heat-resisting organic resin such as siloxane;inorganic insulating material (SiN, SiO, SiON, SiNO, or the like); or astacked layer formed by the foregoing materials can be used. Herein,photosensitive organic resin covered by a silicon nitride film is used.As the foregoing insulator, any of a negative type photosensitive resinthat becomes insoluble to etchant by light and a positive typephotosensitive resin that becomes dissoluble to etchant by light can beused.

The shape of a side face of the bank layer 409 is not especiallyrestricted. The bank layer 409 has preferably an S shape as shown inFIGS. 4A, 4B and the like. In other words, the bank layer 409 haspreferably an inflection point at the side face of the bank layer 409.Accordingly, the coverage of a first light-emitting layer 103, anintermediate conductive layer (an electron-injecting layer 104 and ahole-injecting layer 105), a second light-emitting layer 106, thecathode 107 and the like that are formed over the pixel electrode (theanode 102) can be improved. Note that the insulator may be formed tohave a curved upper edge portion having a radius of curvature, withoutbeing limited to the above described shape.

The first light-emitting layer 103, the intermediate conductive layer(the electron-injecting layer 104 and the hole-injecting layer 105), thesecond light-emitting layer 106, the cathode 107 and the like are formedover the anode 102 according to Embodiment described above. Note that apassivation film for blocking impurities such as water and oxygen intothe light-emitting layer and the like, a layer for relaxing stress tothe passivation film, a low refractive index layer having a lowrefractive index of air and the like may be formed over the cathode.

The light-emitting element according to the present invention is a topemission type which emits light through the cathode 107. An aluminumfilm having a thickness of 1 to 10 nm or an aluminum film slightlycontaining Li may be used for the cathode 107. When using an aluminumfilm as the cathode 107, a material except an oxide can be used as amaterial being in contact with the second light-emitting layer 106, andthus the reliability of a light-emitting device can be improved. Beforeforming the aluminum film having a thickness of 1 to 10 nm, a layerhaving a light-transmitting property (thickness of 1 to 5 nm) made fromCaF₂, MgF₂, or BaF₂ may be formed as a cathode buffer layer. In order toreduce the resistance of the cathode 107, the cathode 107 may be formedto have a stacked layer structure of a thin metal film having athickness of 1 to 10 nm and a transparent conductive film (ITO, indiumoxide-zinc oxide alloy (In₂O₃—ZnO), zinc oxide (ZnO), or the like).Alternatively, in order to reduce the resistance of the cathode, anauxiliary electrode may be provided over the cathode 107 in a regionthat does not become a light-emitting region. The cathode may be formedselectively by using a resistance heating method by vapor depositionusing an evaporation mask.

In the structure of FIG. 4A, the wiring 414 is formed through theopening portion formed in the second interlayer insulating film 412 andconnected to the anode 102. However, a third interlayer insulating filmand the anode 102 may be formed over the second interlayer insulatingfilm 412, and the wiring 412 may be connected to the anode 102 throughan opening portion formed in the third interlayer insulating film. Thethird interlayer insulating film may be formed in the same manner as thesecond interlayer insulating film. In this case, the structure can bedesigned more freely without any limitation on a region for forming thelight-emitting element 313 due to a region for forming the transistor312 or the wiring 414. Accordingly, a display device having a desiredaperture ratio can be easily obtained.

The position where a connection film 407 is to be provided is notlimited to that shown in FIG. 4A, and for example, the connection film407 may be formed to be directly connected to the wiring 414 over thesecond interlayer insulating film 412. In addition, a space 418 may befilled with resin or the like.

A structure shown in FIG. 4B is described hereinafter. FIG. 4B shows alight-emitting region 400 of a dual emission light-emitting device towhich a light-emitting element according to the present invention isapplied. In FIG. 4B, light-emitting elements 313 corresponding to R, Qand B are provided. The light-emitting layers corresponding to R, G, andB can be formed according to Embodiment described above.

Moreover, since the light-emitting device shown in FIG. 4B is adual-emission type, the anode 102 and the cathode 107 are required totransmit light. Therefore, ITO is typically used for the anode 102.Instead of ITO, a transparent conductive film such as ITSO (indium tinsilicon oxide) which is a mixture of ITO and silicon oxide), ZnO (zincoxide), GZO (gallium-doped zinc oxide), or IZO (indium zinc oxide) whichis a mixture of indium oxide and zinc oxide of approximately 1 to 20%)can be used.

On the other hand, a transparent conductive film formed byco-evaporation of an element such as Al, AlLi, MgAg, MgIn, Ca, or anelement belonging to 1 or 2 group in the periodic table and aluminum canbe used as the cathode 107. These materials are suitable for a cathodematerial because they have low work functions and electrons are easilyextracted therefrom. Note that the materials are required to be ultrathin so as to transmit light. A transparent conductive film such as ITOcan be used as the cathode 107; however, a transparent conductive filmitself cannot function as the cathode. Thus, a thin film of Li or thelike is preferably formed between the ITO and the second light-emittinglayer 106.

The first light emitting layer 103, the intermediate conductive layer(in other words, the electron-injecting layer 104 and the hole-injectinglayer 105), the second light emitting layer 106, the cathode 107 and thelike are formed over the anode 102 according to Embodiment describedabove. Note that a passivation film for blocking impurities such aswater and oxygen into the light-emitting layer and the like, a layer forrelaxing stress to the passivation film, a low refractive index layerhaving a low refractive index of air and the like may be formed over thecathode.

The present invention shown in FIG. 4B has a structure in which, as thewhole or a portion of the second interlayer insulating film and the banklayer, an interlayer insulating film 417 having a light-shieldingproperty (hereinafter, a light-shielding interlayer insulating film) anda bank layer 416 having a light-shielding property (hereinafter, alight-shielding bank layer) formed by adding carbon or metal particlesto an organic material such as acrylic, polyimide, or siloxane, areused. An opening portion for transmitting light from the light-emittinglayer is provided in the light-shielding interlayer insulating film 417,and the opening portion is filled with a light-transmitting resin 415such as acrylic, polyimide, or siloxane.

The light-shielding interlayer insulating film 417 and thelight-shielding bank layer 416 are formed in such a way that carbon andmetal particles having a light-shielding property are added to anorganic material such as acrylic, polyimide, or siloxane, and thematerial is agitated by using a shaker or an ultrasonic shaker, then,the agitated material is filtrated when needed, and then is spin-coated.When adding carbon particles or metal particles to an organic material,a surface active agent, a dispersing agent, or the like may be added tothe organic material in order that these particles are mixed uniformly.In the case that the carbon particles are added, the amount of the addedcarbon particles may be controlled so that the concentration of thecarbon particles is 5 to 15 atomic % by weight. Further, the thin filmformed by a spin coating itself without change can be used. However, thethin film may be baked to be hardened. The transmittance and reflectanceof the formed thin film each are 0% or approximately 0%.

The materials and structures of the first interlayer insulating film411, the wiring 414 and the like are based on the structure of thepresent invention shown in FIG. 4A. In addition, a third interlayerinsulating film may be formed separately over the second interlayerinsulating film so that the whole or a portion thereof shields light.

In the dual-emission display device shown in FIG. 4B, a light-shieldinginterlayer insulating film 417 and a light-shielding bank layer 416 areprovided, thereby preventing outlines of pixels from becoming blur(not-cleared) due to unnecessary light from the light-emitting layer(including light produced as the result of reflection of light emitteddownward). In other words, the light-shielding insulating film absorbsunnecessary light, and thus the outlines of the pixels are clear and animage with high-quality can be displayed. Moreover, since the influenceof the unnecessary light can be suppressed by arranging thelight-shielding film, a polarizing plate is not needed and reduction insize, weight and thickness can be achieved. Moreover, the unnecessarylight can be prevented from being leaked into, in particular, a regionof a pixel where transistors are formed, and active matrix drive can beconducted with high-reliable transistors.

In FIGS. 4A and 4B, as described in Embodiment, when the light emittedfrom the light-emitting element 313 is light of white, color filters forR, G and B are provided in each pixel portion of the display device,thereby obtaining a full-color display device. The color filters can beformed using a known material and by a known method. In thedual-emission light-emitting device, the opening portion provided in thesecond interlayer insulating film 412 (or a light-shielding interlayerinsulating film 417) is filled with light-transmitting resin includingthe coloring pigments of red, green and blue, and thus a color filter ofa lower side (or a film serving as a color filter) is formed. It ispreferable that the resin including coloring pigment is selectivelyformed by a droplet-discharging method. Further, a color filter of anupper side corresponding to the color filter of the lower side is formedusing a known material on the opposite substrate side by a known method(not shown).

In general, when a color filter is formed, a black matrix (a lattice- orstripe-like light-shielding film for optically separating pixels of R, Gand B) is formed in the periphery thereof. However, in the presentinvention according to the structure in FIG. 4B, the light-shieldingbank layer 416 or the light-shielding interlayer insulating film 417 isformed in a portion where light is to be shielded, instead of using theblack matrix. Therefore, manufacturing yields are improved sincealignment can be more readily carried out, and the cost can be morereduced since an extra process is not required, as compared with thecase of forming a black matrix separately.

In this example, the display panel can exert such effects of preventingadverse effects due to unnecessary light from a light-emitting layer, ifat least either of the light-shielding interlayer insulating film 417and the light-shielding bank layer 416 is formed. Needless to say, it isdesirable that both the light-shielding interlayer insulating film 417and the light-shielding bank layer 416 are formed. Characteristic pointsin the present invention related to FIGS. 4A and 4B can be replaced orcombined with each other and implemented.

In this example, a structure in which the anode 102 and the cathode 107are counterchanged may be adopted. In this case, the polarity of thetransistor 312 connected to the cathode 107 may be reverse. This examplecan be freely combined with Embodiment and other Examples.

EXAMPLE 2

In this example, an example of a pixel circuit that can be applied tothe present invention except the pixel circuit shown in FIG. 3A isexplained with reference to FIGS. 5A and 5B. FIG. 5A shows a pixelcircuit having a structure in which a transistor 340 for erasing and agate wiring Ry for erasing are added to the pixel 310 that is shown inFIG. 3A. Since current does not flow to the light-emitting element 313forcibly by the arrangement of the transistor 340, a lightning periodcan be started simultaneously with or immediately after starting awriting period without waiting for writing signals into all of pixels310. Therefore, a duty ratio is improved, and thus a moving image can beespecially displayed so well.

FIG. 5B shows a pixel circuit in which a transistor 312 of the pixel 310shown in FIG. 3A is omitted and transistors 341, 342, and a power sourceline Vax (x is a natural number, 1≦x≦1) are provided anew. The powersource line Vax is connected to a power source 343. In this structure,the potential of a gate electrode of the transistor 341 is fixed and thetransistor 341 is operated in a saturation region by connecting the gateelectrode of the transistor 341 to the power source line Vax that iskept at constant potential. Further, the transistor 342 is operated in alinear region and a video signal including information of lighting andnon-lighting of a pixel is inputted to the gate electrode of thetransistor 342. Since the value of source-drain voltage of thetransistor 342 operating in the linear region is small, slight variationof the gate-source voltage of the transistor 342 does not influence thecurrent value of the light-emitting element 313. Therefore, the value ofcurrent flowing through the light-emitting element 313 is determineddepending on the transistor 341 operating in the saturation region. Thepresent invention having the foregoing configuration can improveluminance variation of the light-emitting element 313 due tocharacteristic variation of the transistor 341 to improve image quality.This example can be freely combined with Embodiment and other examples.

EXAMPLE 3

In this example, stacked layer structures of the wiring 414 (including asecond power source 318 through this example) and the pixel electrode(anode or cathode) in the foregoing example are explained with referenceto FIGS. 6A to 6D. FIGS. 6A to 6D each show only a part of alight-emitting element of a pixel region. In the FIGS. 6A to 6D, asecond light-emitting layer, an intermediate conductive layer and thelike are not shown.

FIG. 6A shows the case that the wiring is formed to have a stacked layerstructure of Mo 600 and an alloy containing aluminum 601 and the pixelelectrode (e.g., anode 102 through this example) is formed using ITO602. As the alloy containing aluminum 601, aluminum containing carbon,nickel, cobalt, iron, silicon, or the like is preferably used. It ispreferable that the rate of content of carbon is preferably 0.1 to 3.0atomic %; at least one kind of nickel, cobalt, and iron, 0.5 to 7.0atomic %; and silicon, 0.5 to 2.0 atomic %. The material has onecharacteristic of having low resistance of 3.0 to 5.0 Ωcm. Here, the Mo600 serves as a barrier metal.

In the case that at least one kind of nickel, cobalt, and iron iscontained in the alloy 601 containing aluminum at 0.5% or more,potential of the alloy 601 can be made almost equal to electrodepotential of the ITO 602, and thus the alloy can make directly contactto the ITO 602. Further, heat resistance of the alloy containingaluminum 601 is increased. By setting the rate of content of carbon 0.1%or more, occurrence of hillock can be prevented. There is an advantagethat hillock is also prevented by mixing silicon into the alloy 601 orheating the alloy 601 at high temperature.

In FIG. 6B, an alloy containing aluminum 603 is used as a wiring and ITO602 is used as a pixel electrode. Here, the alloy containing aluminum603 contains at least nickel. After forming the alloy containingaluminum 603, nickel contained in the alloy seeps out to reactchemically with silicon of a silicon semiconductor layer 608 of anactive element (e.g., a TFT) for driving the pixel region. Thus, anickel silicide 607 is formed. Therefore, there is an advantage ofimproving a conjugative property by the nickel silicide.

In FIG. 6C, an alloy containing aluminum 604 as a wiring and ITO 605 asa pixel electrode are stacked. It can be experimentally found thatflatness is drastically improved especially in the case of a stackedlayer structure of the alloy 604 containing aluminum and the ITO 605 isadopted. For example, the flatness thereof is twice as favorable as thatof a stacked layer structure of a wiring formed by stacking TiN over anAl—Si alloy and ITO, and a stacked layer structure of a wiring formed bystacking TiN over an Al—Si alloy and ITSO.

In FIG. 6D, an alloy containing aluminum 604 and an alloy containingaluminum 606 are used as a wiring and a pixel electrode, respectively.

Since the alloy containing aluminum can be easily pattern-formed by awet etching method, the alloy containing aluminum can be widely usedwithout being limited to a wiring or a pixel electrode. The alloycontaining aluminum has high reflectivity, and thus it is preferablyused in a top emission display device. In the case of a bottom emissionor dual emission display device, the wiring or the pixel electrode isrequired to be formed as a thin film so as to transmit lighttherethrough. This example can be freely combined with Embodiment orother examples.

EXAMPLE 4

As an electronic device using a display device including a pixel regionhaving a light-emitting element according to the present invention, atelevision device (TV, TV receiver), a camera such as a digital cameraor a digital video camera, a portable phone device (such as a cellularphone), a portable information terminal such as a personal digitalassistant (PDA), a portable game machine, a monitor, a computer, a soundplayback device such as a car audio, an image playback device having arecording medium such as a domestic game machine, and the like can benominated. Specific examples thereof are explained with reference toFIGS. 7A to 7F.

A portable information terminal using a display device according to thepresent invention shown in FIG. 7A includes a main body 9201, a displayportion 9202 and the like, and can display a high resolution imageaccording to the present invention. A digital camera using a displaydevice according to the present invention shown in FIG. 7B includesdisplay portions 9701, 9702 and the like, and can display a highresolution image according to the present invention. A portable terminalusing a display device according to the present invention shown in FIG.7C includes a main body 9101, a display portion 9102 and the like, andcan display a high resolution image according to the present invention.A portable television device using a display device according to thepresent invention shown in FIG. 7D includes a main body 9301, a displayportion 9302, and the like and can display a high resolution imageaccording to the present invention. A laptop personal computer using adisplay device according to the present invention shown in FIG. 7Eincludes a main body 9401, a display portion 9402 and the like, and candisplay a high resolution image according to the present invention. Atelevision device using a display device according to the presentinvention shown in FIG. 7F includes a main body 9501, a display portion9502 and the like, and can display a high resolution image according tothe present invention. In the case that an interlayer insulating filmhaving a light-shielding property or a bank layer having alight-shielding property is provided as in the above examples, aninfluence due to unnecessary light can be suppressed, and thus apolarizing plate is not required, which results in reduction of thesize, the weight, and the thickness.

A brief explanation of the main structure of the television device isgiven with reference to a block diagram in FIG. 8. In FIG. 8, an ELdisplay panel 701 is manufactured using a display device according tothe present invention. As a connecting method of the EL display panel701 and an external circuit, are given the following methods asexamples: 1: a method of integrating a pixel portion of a display paneland a scanning line driver circuit 703 over a substrate and furthermounting a signal line driver circuit 702 separately as a driver IC, 2:a method in which only a pixel portion of a display panel is formed anda scanning line driver circuit 703 and a signal line driver circuit 702are mounted by a TAB method, and 3: a method in which a pixel portion ofa display panel and a scanning line driver circuit 703 and a signal linedriver circuit 702 are each mounted in the periphery of the pixelportion by a COG method, and other methods. Any method thereof may beemployed.

The structure of other external circuits includes a video wave amplifiercircuit 705 that amplifies a video signal among signals received by atuner 704; a video signal processing circuit 706 that converts thesignal outputted from the video wave amplifier circuit 705 into a colorsignal corresponding to each color of red, green, and blue; a controlcircuit 707 that converts the video signal to input specification of thedriver IC; and the like on an input side of video signals. The controlcircuit 707 outputs signals to a scanning line side and a signal lineside, respectively. In the case of digital driving, a signal dividingcircuit 708 may be provided on the signal line side to supply an inputdigital signal by dividing the input digital signal into m pieces.

Among signals received by the tuner 704, an audio signal is transmittedto an audio wave amplifier circuit 709 and the output signal is suppliedto a speaker 713 via an audio signal processing circuit 710. Acontrolling circuit 711 receives information on controlling a receivingstation (received frequency) or volume from an input portion 712 andsends a signal to the tuner 704 and the audio signal processing circuit710.

The television device as shown in FIG. 7F can be completed by installingsuch external circuits and the EL display panel in a casing. It is clearthat the present invention is not limited to the television device butcan be used in various devices, especially as a large display mediumsuch as a monitor of a personal computer, an information board in astation or airport, or an advertisement board in the street. Thisexample can be freely combined with Embodiment and other examples.

EXAMPLE 5

A display device according to the present invention can be used as an IDcard capable of sending and receiving data without contact by installinga functional circuit such as a memory or a processing circuit, or anantenna coil. An example of the structure of such an ID card isexplained with reference to drawings.

FIG. 9A shows one mode of an ID card incorporating a display deviceaccording to the present invention. The ID card shown in FIG. 9A is anon-contact type ID card that sends and receives data without contactto/from a reader/writer that is a terminal device. Reference numeral 801denotes a card main body, and reference numeral 802 denotes a pixelportion of a display device installed in the card main body 801.

FIG. 9B shows the structure of a card substrate 803 included in the cardmain body 801 shown in FIG. 9A. An ID chip 804 formed of a thinsemiconductor film and a display device 805 according to theabove-described embodiment or examples are attached onto the cardsubstrate 803. Both of the ID chip 804 and the display device 805 areformed over a substrate prepared separately and then transferred ontothe card substrate 803. As a method of transferring, a thin filmintegrated circuit formed with a number of TFTs is manufactured, and thethin film integrated circuit is attached with a small vacuum tweezers orthe like, or selectively attached by a UV light irradiation method. Apixel portion or a driver circuit unit in the display device can betransferred in the same manner. A portion that includes the ID chip 804and the display device 805 and that is formed using a semiconductor thinfilm and then transferred onto the card substrate is referred to as athin film portion 807.

An integrated circuit 806 manufactured using a TFT is mounted on thecard substrate 803. A method of mounting the integrated circuit 806 isnot especially restricted. A known method such as a COG method, a wirebonding method or a TAB method can be used. The integrated circuit 806is electrically connected to the thin film portion 807 by a wiring 808that is provided on the card substrate 803.

An antenna coil 809 electrically connected to the integrated circuit 806is formed on the card substrate 803. Since data can be sent and receivedby the antenna coil 809 without contact with electromagnetic induction,a non-contact type ID card is less damaged due to physical abrasion thana contact type ID card. The non-contact type ID card can be used as atag (wireless tag) that controls information without contact. Thenon-contact type ID card can manage so much larger amount of informationthan a bare code that can read information similarly without contact.Further, the distance between an object and a terminal device that canread information can be made longer than that in the case of the barcode.

FIG. 9B shows an example of forming the antenna coil 809 over the cardsubstrate 803; however, an antenna coil manufactured separately can bemounted on the card substrate 803. For example, a copper wire or thelike that has wound into a coil form and pressed between two plasticfilms having thicknesses of approximately 100 μm can be used as anantenna coil. Alternatively, an antenna coil can be formed in the thinfilm integrated circuit. One antenna coil 809 is used in one ID card inFIG. 9B; however, a plurality of the antenna coils 809 may be used.

FIGS. 9A and 9B show a mode of the ID card incorporating the displaydevice 805; however, the present invention is not limited thereto, thedisplay device is not always required to be provided. However, byproviding the display device, the data of a photograph of the face canbe displayed on the display device, thereby making replacing thephotograph of the face more difficult as compared with a printingmethod. The display device can display information except the photographof the face, which can improve the function of the ID card.

As the card substrate 803, a plastic substrate having flexibility can beused. ARTON made from norbornene resin having a polar group, which ismanufactured by JSR Corporation, can be used as the plastic substrate.Further, a plastic substrate such as polyethylene terephthalate (PET),polyether sulfone (PBS), polyethylene naphthalate (PEN), polycarbonate(PC), nylon, polyetheretherketone (PEEK), polysulfone (PSF),polyetherimide (PEI), polyarylate (PAR), polybutylene terephthalate(PBT), or polyimide can be used.

In this example, the electrical connection of an ID chip and a thin filmintegrated circuit is not limited to the modes shown in FIGS. 9A and 9B.For example, a terminal of the ID chip can be directly connected to aterminal of the thin film integrated circuit by anisotropic conductiveresin, solder or the like. In FIGS. 9A and 9B, the thin film integratedcircuit and the wiring provided to the card substrate can be connectedwith each other by a wire bonding method, a flip chip method using asolder ball, or connected directly with each other by anisotropicconductive resin, solder or the like. Further, the display deviceaccording to the present invention can be used by being built into asemiconductor device such as an ID tag, a wireless chip, or a wirelesstag as well as an ID card.

EXAMPLE 6

The light-emitting element according to the present invention asdescribed above can be applied to a pixel portion of a light-emittingdevice having a display function or a lighting portion of alight-emitting device having a lighting function. In this example, acircuit configuration and a driving method of the light-emitting devicehaving a display function are explained with reference to FIGS. 10 to13.

FIG. 10 is a schematic view of a top face of a light-emitting deviceaccording to the present invention. A pixel portion 6511, a sourcesignal line driver circuit 6512, a writing gate signal line drivercircuit 6513, and an erasing gate signal line driver circuit 6514 areprovided on a substrate 6500 in FIG. 10. The source signal line drivercircuit 6512, the writing gate signal line driver circuit 6513, and theerasing gate signal line driver circuit 6514 are each connected to anFPC (flexible printed circuit) 6503 that is an external input terminalvia a wiring group. Each of the source signal line driver circuit 6512,the writing gate signal line driver circuit 6513, and the erasing gatesignal line driver circuit 6514 receives a video signal, a clock signal,a start signal, a reset signal, and the like from the FPC 6503. Aprinted wiring board (PWB) 6504 is attached to the FPC 6503. The drivercircuit portion is not always required to be provided on the samesubstrate as the pixel portion 6511. For example, the driver circuitportion may be formed outside the substrate by using TCP or the likethat is formed by mounting an IC chip on an FPC provided with a wiringpattern.

In the pixel portion 6511, a plurality of source signal lines extendingin a column direction are arranged in a row direction. Current supplylines are also arranged in the row direction. In the pixel portion 6511,a plurality of gate signal lines extending in the row direction arearranged in the column direction. In the pixel portion 6511, a pluralityof pixel circuits including a light-emitting element are arranged.

FIG. 11 shows a circuit for operating one pixel. The circuit shown inFIG. 11 includes a first transistor 901, a second transistor 902, and alight-emitting element 903. Each of the first transistor 901 and thesecond transistor 902 is a three-terminal element including a gateelectrode, a drain region, and a source region, in which a channelregion is formed between the drain region and the source region. Becausethe source region and the drain region are interchanged depending on thestructure, an operational condition or the like of the transistor, it isdifficult to distinguish the source region from the drain region. Inthis example, regions to serve as a source and a drain are referred toas a first electrode and a second electrode.

A gate signal line 911 and a writing gate signal line driver circuit 913are provided to be electrically connected or not to be electricallyconnected with each other via a switch 918. The gate signal line 911 andan erasing gate signal line driver circuit 914 are provided to beelectrically connected or not to be electrically connected with eachother via a switch 919. A source signal line 912 is provided toelectrically connect to either a source signal line driver circuit 915or a power source 916 via a switch 920. The gate of the first transistor901 is electrically connected to the gate signal line 911. The firstelectrode of the first transistor 901 is electrically connected to thesource signal line 912, and the second electrode of the first transistor901 is electrically connected to the gate electrode of the secondtransistor 902. The first electrode of the second transistor 902 iselectrically connected to a current supply line 917, and the secondelectrode of the second transistor 902 is electrically connected to oneelectrode included in the light-emitting element 903. The switch 918 maybe included in the writing gate signal line driver circuit 913. Theswitch 919 may also be included in the erasing gate signal line drivercircuit 914. The switch 920 may also be included in the source signalline driver circuit 915.

The arrangement of a transistor, a light-emitting element and the likein the pixel portion is not especially restricted. For example, theelements can be arranged as shown in a top view of FIG. 12. In FIG. 12,a first electrode of a first transistor 1001 is connected to a sourcesignal line 1004, and a second electrode of the first transistor 1001 isconnected to a gate electrode of the second transistor 1002. A firstelectrode of the second transistor 1002 is connected to a current supplyline 1005, and a second electrode of the second transistor is connectedto an electrode 1006 of a light-emitting element. A part of a gatesignal line 1003 serves as a gate electrode of the first transistor1001.

Next, a driving method is explained. FIG. 13 is an explanatory view ofan operation of a frame with time. In FIG. 13, the abscissa-axisdirection represents time passage, whereas the ordinate-axis directionrepresents scanning stages of a gate signal line.

When an image is displayed with a light-emitting device according to thepresent invention, a rewriting operation and a displaying operation arerepeatedly carried out in a display period. The number of rewritingoperations is not especially restricted; however, the rewritingoperation is preferably performed approximately sixty times per onesecond so that a person who watches the image does not find flickering.Herein, the period when the operations of rewriting and displaying ofone image (one frame) are carried out is referred to as one frameperiod.

One frame period is time-divided into four sub frame periods 501, 502,503, and 504 including writing periods 501 a, 502 a, 503 a, and 504 a,and retention periods 501 b, 502 b, 503 b, and 504 b. A light-emittingelement that receives a light-emission signal emits light in theretention period. The length ratio of the retention period in each ofthe first sub frame period 501, the second sub frame period 502, thethird sub frame period 503, and the fourth sub frame period 504 is2³:2²:2¹:2⁰=8:4:2:1. Accordingly, a 4-bit gray scale can be realized.The number of bits or gray scale levels is not limited thereto. Forinstance, an 8-bit gray scale can be offered by providing eight subframe periods.

An operation in one frame period is explained. Firstly, a writingoperation is carried out from the first row to the last row sequentiallyin the sub frame period 501. Therefore, the starling time of a writingperiod is different depending on the rows. The retention period 501 bstarts in the row where the writing period 501 a is completed. In theretention period, a light-emitting element that receives alight-emission signal emits light. The sub frame period 502 starts inthe row where the retention period 501 b is completed, and a writingoperation is carried out from the first row to the last row sequentiallyas is the case with the sub frame period 501. Operations as noted aboveare repeatedly carried out to finish the retention period 504 b of thesub frame period 504. When an operation in the sub frame period 504 isfinished, an operation in the next frame period is started. The sum ofemitting time in each of the sub frame periods is an emitting time ofeach light-emitting element in one frame period. By varying the emittingtime for each light-emitting element to be variously combined in onepixel, various colors can be displayed with different brightness andchromaticity.

When a retention period in the row where writing has been finishedbefore finishing the writing of the last row and the retention periodhas started is intended to be terminated forcibly like the sub frameperiod 504, an erasing period 504 c is provided after the retentionperiod 504 b to control so that the light-emission is forcibly stopped.The row where the light-emission is forcibly stopped does not emit lightduring a fixed period (the period is referred to as a non-light emissionperiod 504 d). Upon finishing the writing period of the last row, thenext writing period (or a frame period) starts from the first row. Inorder that writing is carried out in a pixel of a certain row and anerasing signal for allowing a pixel not to emit light is input into apixel of a certain row, as shown in FIG. 15, one horizontal period isdivided into two periods, either of which is used to write and the otherof which is used to erase. In the divided horizontal period, each gatesignal line 911 is selected to input a corresponding signal to thesource signal line 912. For instance, the former horizontal periodselects the i-th row, and the later horizontal period selects the j-throw in one horizontal period. Hence, it is possible to operate as if tworows are selected simultaneously in the horizontal period. That is, avideo signal is written into a pixel in the writing periods 501 a to 504a using a writing period of each horizontal period, and at this time, apixel is not selected in an erasing period in the horizontal period. Asignal written into a pixel in the erasing period 504 c is erased byusing an erasing period in another horizontal period, and at this time,a pixel is not selected in a writing period in the horizontal period.Therefore, a display device having a pixel with a high aperture ratiocan be provided and manufacturing yields can be improved.

In this example, the sub frame periods 501 to 504 are arranged in theorder from the longest retention period; however, the present inventionis not limited thereto. For instance, the sub frame periods 501 to 504may be arranged in the order from the shortest retention period. The subframe periods 501 to 504 may be arranged at random combining short subframe periods and long sub frame periods. The sub frame period may befurther divided into a plurality of frame periods. That is, scanning ofthe gate signal line can be carried out a plurality of times during theperiod of giving the same video signal.

An operation in a writing period and an erasing period of the circuitshown in FIG. 11 is explained. First, an operation in the writing periodis explained. In the writing period, the gate signal line 911 in thei-th row (i is a natural number) is electrically connected to thewriting gate signal line driver circuit 913 via the switch 918. The gatesignal line 911 is not connected to the erasing gate signal line drivercircuit 914. The source signal line 912 is electrically connected to thesource signal line driver circuit 915 via the switch 920. A signal isinputted to the gate of the first transistor 901 connected to the gatesignal line 911 in the i-th row, and the first transistor 901 is turnedON. At this time, video signals are simultaneously inputted to thesource signal lines in the first column to the last column. Videosignals inputted from the source signal line 912 at each column areindependent from each other. The video signal inputted from the sourcesignal line 912 is inputted to the gate electrode of the secondtransistor 902 via the first transistor 901 connected to each sourcesignal line. The signal inputted to the gate electrode of the secondtransistor 902 controls ON/OFF of the second transistor 902. When thesecond transistor 902 is turned ON, voltage is applied to thelight-emitting element 903 and current flows to the light-emittingelement 903. Emission or non-emission of the light-emitting element 903is determined depending on a signal inputted to the gate electrode ofthe second transistor 902. For example, in the case that the secondtransistor 902 is a p-channel type, the light-emitting element 903 emitslight when a Low Level signal is inputted to the gate electrode of thesecond transistor 902. On the other hand, in the case that the secondtransistor 902 is an n-channel type, the light-emitting element 903emits light when a High Level signal is inputted to the gate electrodeof the second transistor 902.

Then, an operation in the erasing period is explained. In the erasingperiod, the gate signal line 911 of the j-th row (j is a natural number)is electrically connected to the erasing gate signal line driver circuit914 via the switch 919. The gate signal line 911 is not connected to thewriting gate signal line driver circuit 913. The source signal line 912is electrically connected to the power source 916 via the switch 920. Asignal is inputted to the gate of the first transistor 901 connected tothe gate signal line 911 in the j-th row, and the first transistor 901is turned ON. At this time, erase signals are simultaneously inputted tothe source signal lines in the first column to the last column. Theerase signal inputted from the source signal line 912 is inputted to thegate electrode of the second transistor 902 via the first transistor 901connected to each source signal line. By the erase signal inputted tothe gate electrode of the second transistor 902, the second transistor902 is turned OFF and current supply from the current supply line 917 tothe light-emitting element 903 is stopped. The light-emitting element903 does not emit light forcibly. For example, in the case that thesecond transistor 902 is a p-channel type, the light-emitting element903 does not emit light when a High Level signal is inputted to the gateelectrode of the second transistor 902. On the other hand, in the casethat the second transistor 902 is an n-channel type, the light-emittingelement 903 does not emit light when a Low Level signal is inputted tothe gate electrode of the second transistor 902.

In the erasing period, a signal for erasing is inputted to the j-th rowby the operation as described above. However, there is a case that thej-th row is in an erasing period and another row (the i-th row in thisinstance) is in a writing period. In this instance, it is required thata signal for erasing is inputted to the j-th row and a signal forwriting is inputted to the i-th row by utilizing a source signal line ofthe same column. Accordingly, an operation explained as follows ispreferably carried out.

Immediately after the light-emitting element 903 in the (j−1)-th row isbrought into a non emission state by the operation in the erase state,the gate signal line 911 is disconnected from the erasing gate signalline driver circuit 914, and the source signal line 912 is connected tothe source signal line driver circuit 915 by changing the switch 920. Aswell as connecting the source signal line 912 to the source signal linedriver circuit 915, the gate signal line 911 is connected to the writinggate signal line driver circuit 913 by changing the switch 918. A signalis selectively inputted to the gate signal line 911 in the i-th row fromthe writing gate signal line driver circuit 913, and when the firsttransistor 901 is turned ON, video signals for writing are inputted tothe source signal lines 912 in the first column to the last column fromthe source signal line driver circuit 915. The light-emitting element903 in the i-th row emits light or no light depending on the videosignal.

Immediately after finishing the writing period of the i-th row as notedabove, an erasing period in the j-th row starts. Hence, the gate signalline and the writing gate signal driver circuit 913 are disconnected bychanging the switch 918, and the source signal line 912 and the powersource 916 are connected by changing the switch 920. Further, the gatesignal line 911 and the writing gate signal line driver circuit 913 aredisconnected, and the gate signal line 911 is connected to the erasinggate signal line driver circuit 914 by changing the switch 919. When asignal is selectively inputted to the gate signal line 911 in the j-throw from the erasing gate signal line driver circuit 914, and the firsttransistor 901 is turned ON, an erase signal is inputted from the powersource 916. By the erase signal, the light-emitting element 903 does notemit light forcibly. Immediately after finishing the erasing period inthe j-th row, a writing period in the (i+1)-th row starts. Hereinafter,an erasing period and a writing period may be carried out repeatedly tooperate to complete an erasing period of the last row.

In this example, a mode in which the writing period in the i-th row isprovided between the erasing period of the (j−1)-th row and the erasingperiod of the j-th row is explained. Without being limited to this,however, the writing period of the i-th row may be provided between theerasing period of the j-th row and the erasing period of the (j+1)-throw.

In this example, when providing the non-light emission period 504 d asin the sub frame period 504, an operation of disconnecting the erasinggate signal line driver circuit 914 from a certain gate signal line andconnecting the writing gate signal line driver circuit 913 to anothergate signal line is repeatedly carried out. Such an operation may becarried out in a frame period that is not provided with a non-lightemission period. This example can be freely combined with Embodiment andthe other examples.

One feature of a light-emitting element according to the presentinvention is that, in an EL element having a plurality of light-emittinglayers between a pixel electrode and an opposite electrode, anintermediate conductive layer is formed between each light-emittinglayer, and in the intermediate conductive layer (at least oneintermediate conductive layer in the case where plural intermediateconductive layers are formed), either a hole-injecting layer or anelectron-injecting layer is formed to be island-like, instead of beingfilm-like. Various effects can be obtained by employing such astructure, such as the effect that transparency of a material for theelectron-injecting (or hole-injecting) layer of an intermediateconductive layer is not required to be considered; the effect that lightfrom the light-emitting layer is not mostly absorbed into theintermediate conductive layer; the effect that the crystallinity ofmaterials of intermediate conductive layers is not needed to beconsidered; and the effect that manufacturing time of an element can beshortened.

A light-emitting element having the operation effects can be adopted ina display device typified by an EL display. Such display devices areclassified into two type systems, namely, a system in which alight-emitting layer and an intermediate conductive layer are formedbetween two kinds of stripe-shaped electrodes that are arranged to be atright angels to each other (simple active matrix system), and a systemin which a light-emitting layer and an intermediate conductive layer areformed between a pixel electrode and an opposite electrode that areconnected to TFTs and arranged in matrix (active matrix system). Alight-emitting element according to the present invention can be appliedto the simple matrix type and the active matrix type. Moreover, thedisplay device can be mounted on various electronic devices andubiquitous products such as an ID card, and thus the availability of thepresent invention is wide-ranging. The present application is based onJapanese Priority Application No. 2004-151103 filed on May 20, 2004 withthe Japanese Patent Office, the entire contents of which are herebyincorporated by reference.

1. A light-emitting element comprising: a first electrode; a firstlight-emitting layer over the first electrode; an intermediateconductive layer on the first light-emitting layer; a secondlight-emitting layer on the intermediate conductive layer; and a secondelectrode over the second light-emitting layer, wherein the intermediateconductive layer comprises an electron-injecting layer and ahole-injecting layer that is in contact with the electron-injectinglayer, wherein the electron-injecting layer and the hole-injecting layerare in contact with the first light-emitting layer, and wherein theelectron-injecting layer comprises at least one island-like structure.2. The light-emitting element according to claim 1, wherein theelectron-injecting layer comprises a metal having a low work function.3. The light-emitting element according to claim 1, wherein the firstelectrode is a pixel electrode and the second electrode is an oppositeelectrode.
 4. The light-emitting element according to claim 1, whereinthe hole-injecting layer comprises molybdenum oxide and aromatic amine.5. The light-emitting element according to claim 1, wherein theisland-like structure is dotted in an island-shaped state.
 6. Alight-emitting element comprising: a first electrode; a plurality oflight-emitting layers; a plurality of intermediate conductive layerssandwiched by the plurality of light-emitting layers; and a secondelectrode, wherein the first electrode, the plurality of light-emittinglayers, the plurality of intermediate conductive layers sandwiched bythe plurality of light-emitting layers, the second electrode arestacked, wherein at least one of the intermediate conductive layersincludes an electron-injecting layer and a hole-injecting layer that isin contact with the electron-injecting layer, wherein theelectron-injecting layer and the hole-injecting layer are in contactwith at least one of the plurality of light-emitting layer, and whereinthe electron-injecting layer comprises at least one island-likestructure.
 7. The light-emitting element according to claim 6, whereinthe electron-injecting layer comprises a metal having a low workfunction.
 8. The light-emitting element according to claim 6, whereinthe first electrode is a pixel electrode and the second electrode is anopposite electrode.
 9. The light-emitting element according to claim 6,wherein the hole-injecting layer comprises molybdenum oxide and aromaticamine.
 10. The light-emitting element according to claim 6 wherein theisland-like structure is dotted in an island-shaped state.
 11. Alight-emitting element comprising: an n number of light-emitting layers(where n is an integer equal to or greater than 2) comprising a firstthrough an n-th light-emitting layers between a first electrode and asecond electrode, wherein an intermediate conductive layer is formedbetween a k-th light-emitting layer (where k is an integer of 1≦k≦(n−1))and a (k+1)th light-emitting layer, wherein the intermediate conductivelayer comprises an electron-injecting layer and a hole-injecting layerthat is in contact with the electron-injecting layer, wherein theelectron-injecting layer and the hole-injecting layer are in contactwith the k-th light-emitting layer, and wherein the electron-injectinglayer comprises at least one island-like structure.
 12. Thelight-emitting element according to claim 11, wherein theelectron-injecting layer comprises a metal having a low work function.13. The light-emitting element according to claim 11, wherein the firstelectrode is a pixel electrode and the second electrode is an oppositeelectrode.
 14. The light-emitting element according to claim 11, whereinthe hole-injecting layer comprises molybdenum oxide and aromatic amine.15. The light-emitting element according to claim 11, wherein theisland-like structure is dotted in an island-shaped state.
 16. A displaydevice having a light-emitting element comprising: a first electrode; afirst light-emitting layer over the first electrode; an intermediateconductive layer on the first light-emitting layer; a secondlight-emitting layer on the intermediate conductive layer; and a secondelectrode over the second light-emitting layer, wherein the intermediateconductive layer comprises an electron-injecting layer and ahole-injecting layer that is in contact with the electron-injectinglayer, wherein the electron-injecting layer and the hole-injecting layerare in contact with the first light-emitting layer, wherein theelectron-injecting layer comprises at least one island-like structure,and wherein the light-emitting element is connected to a transistorformed over a substrate through an interlayer insulating film.
 17. Thelight-emitting element according to claim 16, wherein theelectron-injecting layer comprises a metal having a low work function.18. The light-emitting element according to claim 16, wherein the firstelectrode is a pixel electrode and the second electrode is an oppositeelectrode.
 19. The light-emitting element according to claim 16, whereinthe hole-injecting layer comprises molybdenum oxide and aromatic amine.20. The light-emitting element according to claim 16, wherein theisland-like structure is dotted in an island-shaped state.
 21. A displaydevice having a light-emitting element comprising: a first electrode; aplurality of light-emitting layers; a plurality of intermediateconductive layers sandwiched by the plurality of light-emitting layers;and a second electrode, wherein the first electrode, the plurality oflight-emitting layers, the plurality of intermediate conductive layerssandwiched by the plurality of light-emitting layers, the secondelectrode are stacked, wherein at least one of the intermediateconductive layers includes an electron-injecting layer and ahole-injecting layer that is in contact with the electron-injectinglayer, wherein the electron-injecting layer and the hole-injecting layerare in contact with at least one of the plurality of light-emittinglayer, wherein the electron-injecting layer comprises at least oneisland-like structure, and wherein the light-emitting element isconnected to a transistor formed over a substrate through an interlayerinsulating film.
 22. The light-emitting element according to claim 21,wherein the electron-injecting layer comprises a metal having a low workfunction.
 23. The light-emitting element according to claim 21, whereinthe first electrode is a pixel electrode and the second electrode is anopposite electrode.
 24. The light-emitting element according to claim21, wherein the hole-injecting layer comprises molybdenum oxide andaromatic amine.
 25. The light-emitting element according to claim 21,wherein the island-like structure is dotted in an island-shaped state.26. A display device having a light-emitting element comprising: thelight emitting element formed by sequentially laminating an n number oflight-emitting layers (where n is an integer equal to or greater than 2)comprising a first through an n-th light-emitting layers between a firstelectrode and a second electrode, wherein an intermediate conductivelayer is formed between a k-th light-emitting layer (where k is aninteger of 1≦k≦(n−1)) and a (k+1)th light-emitting layer, wherein theintermediate conductive layer comprises an electron-injecting layer anda hole-injecting layer that is in contact with the electron-injectinglayer, wherein the electron-injecting layer and the hole-injecting layerare in contact with the k-th light-emitting layer, wherein theelectron-injecting layer comprises at least one island-like structure,and wherein the light-emitting element is connected to a transistorformed over a substrate through an interlayer insulating film.
 27. Thelight-emitting element according to claim 26, wherein theelectron-injecting layer comprises a metal having a low work function.28. The light-emitting element according to claim 26, wherein the firstelectrode is a pixel electrode and the second electrode is an oppositeelectrode.
 29. The light-emitting element according to claim 26, whereinthe hole-injecting layer comprises molybdenum oxide and aromatic amine.30. The light-emitting element according to claim 26, wherein theisland-like structure is dotted in an island-shaped state.
 31. Thelight-emitting element according to claim 1, wherein at least one of thefirst light-emitting layer and the second light-emitting layer comprisesa hole-transporting layer and an electron-transporting layer.
 32. Thelight-emitting element according to claim 6, wherein at least one of theplurality of light-emitting layers comprises a hole-transporting layerand an electron-transporting layer.
 33. The light-emitting elementaccording to claim 11, wherein at least one of the n number oflight-emitting layers comprises a hole-transporting layer and anelectron-transporting layer.
 34. The light-emitting element according toclaim 16, wherein at least one of the first light-emitting layer and thesecond light-emitting layer comprises a hole-transporting layer and anelectron-transporting layer.
 35. The light-emitting element according toclaim 21, wherein at least one of the plurality of light-emitting layerscomprises a hole-transporting layer and an electron-transporting layer.36. The light-emitting element according to claim 26, wherein at leastone of the n number of light-emitting layers comprises ahole-transporting layer and an electron-transporting layer.
 37. Thelight-emitting element according to claim 1, wherein theelectron-injecting layer comprises lithium and aluminum.
 38. Thelight-emitting element according to claim 6, wherein theelectron-injecting layer comprises lithium and aluminum.
 39. Thelight-emitting element according to claim 11, wherein theelectron-injecting layer comprises lithium and aluminum.
 40. Thelight-emitting element according to claim 16, wherein theelectron-injecting layer comprises lithium and aluminum.
 41. Thelight-emitting element according to claim 21, wherein theelectron-injecting layer comprises lithium and aluminum.
 42. Thelight-emitting element according to claim 26, wherein theelectron-injecting layer comprises lithium and aluminum.